very new to the platform and i'm shocked this still isn't available on garmin. other brands (polar) let you add, customize and fine tune your data fields for each activity and then sync to the device. very easy process with great visual layouts. you need to do this garmin...
I am not sure whether I understand the question in the opening post correctly, but if you want to create customized watch screens, layouts, and even apps with added functionality, then most of the recent Garmin watch models indeed allow it - with the help of the Connect IQ technology. You can either download custom screens and apps from other users, or create your own ones.